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Solid-state thermomagnetic modules operating based on the Nernst–Ettingshausen effects are an alternative to conventional solid-state thermoelectric modules. These modules are appropriate for low-temperature applications where the thermoelectric modules are not efficient. Here, we briefly discuss the application, performance, similarities, and differences of thermoelectric and thermomagnetic materials and modules. We review thermomagnetic module design, Nernst coefficient measurement techniques, and theoretical advances, emphasizing the Nernst effect and factors influencing its response in semimetals such as carrier compensation, Fermi surface, mobility, phonon drag, and Berry curvature. The main objective is to summarize the materials design criteria to achieve high thermomagnetic performance to accelerate thermomagnetic materials discovery. [ABSTRACT FROM AUTHOR]

Mn 3 Sn, a metallic antiferromagnet with an anti-chiral 120 ° spin structure, generates intriguing magneto-transport signatures such as a large anomalous Hall effect, spin-polarized current with novel symmetries, anomalous Nernst effect, and magneto-optic Kerr effect. When grown epitaxially as MgO(110)[001] ∥ Mn 3 Sn(0 1 ¯ 1 ¯ 0)[0001], Mn 3 Sn experiences a uniaxial tensile strain, which changes the bulk sixfold anisotropy to a twofold perpendicular magnetic anisotropy (PMA). Here, we investigate the field-assisted spin–orbit-torque (SOT)-driven dynamics in single-domain Mn 3 Sn with PMA. We find that for non-zero external magnetic fields, the magnetic octupole moment of Mn 3 Sn can be switched between the two stable states if the input current is between two field-dependent critical currents. Below the lower critical current, the magnetic octupole moment exhibits a stationary state in the vicinity of the initial stable state. On the other hand, above the higher critical current, the magnetic octupole moment shows oscillatory dynamics which could, in principle, be tuned from the 100s of megahertz to the terahertz range. We obtain approximate analytic expressions of the two critical currents that agree very well with the numerical simulations for experimentally relevant magnetic fields. We also obtain a unified functional form of the switching time vs the input current for different magnetic fields. Finally, we show that for lower values of Gilbert damping (α ≲ 2 × 10 − 3 ), the critical currents and the final steady states depend significantly on α. The numerical and analytic results presented in our work can be used by both theorists and experimentalists to understand the SOT-driven order dynamics in PMA Mn 3 Sn and design future experiments and devices. [ABSTRACT FROM AUTHOR]

In this study, we systematically investigated the anomalous Nernst effect in perpendicularly magnetized amorphous TbFeCo thin films with various compositions. It was found that the magnitude of the off diagonal thermopower (ODT), which corresponds to the anomalous Nernst effect, can be uniformly explained with respect to the Tb content regardless of the concentration above or below the compensation composition. The maximum ODT of 1.3 μ V/K and the thermoelectric conductivity of 1.59 A/mK at room temperature were obtained, which is more significant than other perpendicular magnetic anisotropy thin films to achieve a large Nernst voltage for roll-type thermoelectric devices. By considering the thermoelectric tensor, Mott's equation, and the scaling law, it was shown both experimentally and theoretically that the magnitudes of the first and second terms contributing to the anomalous Nernst effect are comparable. It was also found that the ODT of TbFeCo thin films is twice or more significant than the product of the Seebeck coefficient and the Hall angle. Furthermore, amorphous metals and Mn-alloys with a large Berry curvature are located above the relation that the ODT is twice the product of the Seebeck coefficient and the Hall angle, which means that amorphous metals are expected to enhance the ANE. [ABSTRACT FROM AUTHOR]

In this study, the influence of carrier doping on the thermo- and galvano-magnetic effects of Bi–Sb alloys was investigated. Seven types of Bi88Sb12 alloys, namely, the undoped and 0.01, 0.02, and 0.04 at. % Te- and Sn-doped alloys, were fabricated via the spark plasma sintering method and solid phase reaction. The magnetic field dependencies of the diagonal resistivity, Hall resistivity, thermal conductivity, Seebeck thermopower, and Nernst thermopower were measured in the range of −5–5 T at 300 K, and the dimensionless figures of merit for the Seebeck and Nernst effects, i.e., the zST and zNT, respectively, were determined. As a result, both the zT values in the magnetic field were improved by the addition of a trace amount of Te. To better understand this behavior, a computational model that qualitatively describes the Seebeck, Nernst, magnetoresistance, and Hall effects, as well as the carrier thermal conductivity of Bi in the magnetic field, was developed based on the Boltzmann equation by considering the relaxation time approximation. The influence of carrier doping on the thermo-magnetic effect was considered by shifting the chemical potential with the rigid-band model in the established computational model. The computational results demonstrated that zST and zNT in the magnetic field were improved by shifting the chemical potential. These findings revealed that carrier doping could be a promising approach to improve the zT, namely, the zST for the Seebeck effect and zNT for the Nernst effect in Bi–Sb alloys in a magnetic field. [ABSTRACT FROM AUTHOR]

Superconducting spintronics explores the interplay between superconductivity and magnetism, sparking substantial interest in nonunitary superconductors as a platform for magneto-superconducting phenomena. However, identifying nonunitary superconductors remains challenging. We demonstrate that spin current driven by thermal gradients sensitively probes the nature of the condensate in nonunitary superconductors. Spin polarization of the condensate in momentum space induces the superconducting spin Seebeck effect, where a spin current is generated along thermal gradients without a thermoelectric charge current. Notably, the nonvanishing superconducting spin Seebeck effect provides a smoking gun evidence of nonunitary superconductivity because it reflects the spin polarization of the condensate in momentum space, irrespective of whether the net pair spin magnetization vanishes. At the same time, the spin chirality of the condensate induces the spin Nernst effect, where a spin current is generated perpendicular to thermal gradients in nonunitary superconductors. These spin caloritronic phenomena offer a definitive probe of nonunitary superconductors. [ABSTRACT FROM AUTHOR]

Spin‐Hall thermopiles have been previously proposed as a means to enhance the spin Seebeck effect (SSE). However, the use of platinum (Pt) for spin detection drives costs high and proves an impediment for scalability. In this work, a cost‐effective spin‐Hall thermopile constructed from opposite spin‐Hall angle ferromagnets, cobalt (Co) and iron (Fe), is reported. The devices are fabricated using a standard sputter‐coated yttrium iron garnet (YIG) substrate that serves as the spin injector, and thermally evaporated Co and Fe strips that enable spin detection. When serially connected to form a (YIG/Co, Fe) thermopile structure, measurements indicate a significant enhancement of the spin voltage that results from the additive spin contributions of the opposite spin‐Hall angle ferromagnets and the anomalous Nernst effect (ANE) that they exhibit. The YIG/Co, Fe thermopile reported here offers a cost‐effective alternative to Pt‐based thermopiles and the possibility of large‐scale implementation to realize future thermoelectric generators. [ABSTRACT FROM AUTHOR]

One of the necessary conditions for achieving high thermoelectric (TE) performance is the large longitudinal (Sxx) and transverse thermopower (Syx), which are closely related to the Fermi level position and the energy‐dependent density of states (DOS) at the Fermi level. Herein, it is demonstrated that HfTe5 has both high‐mobility induced significant quantum oscillations with an ultra‐low quantum limit of 2.7 T, and a significant Lifshitz transition where the Fermi level shows strong temperature dependence. The Landau levels yielded by the magnetic field distort the DOS with many equally‐spaced delta functions and significantly enhance the Sxx and Syx. The drastically enhanced magneto‐longitudinal and transverse TE performance in HfTe5 is achieved under an ultra‐low magnetic field of 1.4 T, which can be easily realized by a permanent magnet. Moreover, the Lifshitz transition further modulates its TE and magneto‐TE performance. Ultimately, the peak values of magneto‐longitudinal and transverse power factors (PF) reach 64 µW cm−1 K−2 at 150 K and 0.9 T and 19 µW cm−1 K−2 at 80 K and 1.4 T, respectively, which are comparable to the best TE materials such as Bi2Te3. This work provides novel methods and significant guidance for the development of TE and magneto‐TE materials. [ABSTRACT FROM AUTHOR]

Photocurrent is a critical observable in a wide range of physical processes across different length scales, serving as a valuable tool for the characterization of semiconductors or two‐dimensional materials. Recently, photocurrent mapping, particularly when combined with magnetothermal transport effects, such as the anomalous Nernst effect (ANE), has been used to image magnetic domains and domain walls. To gain access to photocurrents on the nanoscale, this effect is combined with infrared scattering‐type scanning near‐field optical microscopy, in which strong field enhancement is created at the apex of an atomic force microscopy (AFM) tip, which serves as the confined illumination source creating localized temperature gradients through light absorption in the sample, which can be exploited for ANE detection. Herein, ANE photocurrents generated in a cobalt–iron–boron channel and the optical scattering are compared between various AFM tips, revealing significantly differing behavior for different tips. To gain insight into the origin of these differences, the measurements are further compared to finite element method simulations of tips with varied tip apex radii. [ABSTRACT FROM AUTHOR]

In this paper, we analyzed the influence of the spin Nernst effect on quantum correlation in a layered ferrimagnetic model. In the study of three-dimensional ferrimagnets, the focus is on materials with a specific arrangement of spins, where the neighboring spins are parallel and the others are antiparallel. The anisotropic nature of these materials means that the interactions between spins depend on their relative orientations in different directions. We analyzed the effect of magnon bands induced by the coupling parameters on entanglement negativity. The influence of the coupling parameters of the topologic phase transition on quantum entanglement is investigated as well. Numerical simulations using the Lanczos algorithm and exact diagonalization for different lattice sizes are compared with the results of spin wave theory. [ABSTRACT FROM AUTHOR]

The self-generated magnetic field in three-dimensional (3-D) single-mode ablative Rayleigh–Taylor instability (ARTI) relevant to the acceleration phase of a direct-drive inertial confinement fusion (ICF) implosion is investigated. It is found that stronger magnetic fields up to a few thousand teslas can be generated by 3-D ARTI rather than by its two-dimensional (2-D) counterpart. The Nernst effects significantly alter the magnetic field convection and amplify the magnetic fields. The magnetic field of thousands of teslas yields the Hall parameter of the order of unity, leading to profound magnetized heat flux modification. While the magnetic field significantly accelerates the bubble growth in the short-wavelength 2-D modes through modifying the heat fluxes, the magnetic field mostly accelerates the spike growth but has little influence on the bubble growth in 3-D ARTI. The accelerated growth of spikes in 3-D ARTI is expected to enhance material mixing and degrade ICF implosion performance. This work is focused on a regime relevant to direct-drive ICF parameters at the National Ignition Facility, and it also covers a range of key parameters that are relevant to other ICF designs and hydrodynamic/astrophysical scenarios. [ABSTRACT FROM AUTHOR]

In a three-dimensional Dirac semimetal the time reversal symmetry (TRS) or the inversion symmetry (IS) is not broken. With either of these symmetries broken, the Dirac points in the threedimensional band structure split up into pairs of so-called Weyl points. The ferromagnetic Weyl semimetals (FMWSM), such as Co3Sn2S2, feature pairs of Weyl points characterized by the opposite chiralities. In this communication we study FMWSM based on TRS broken continuum and lattice Hamiltonians. The latter one is more realistic and represents Co3Sn2S2. These models include all essential ingredients leading to the formation of a pair of Weyl nodes and tilted Weyl cones. Our analysis shows a large anomalous Nernst conductivity which is unlocked due to the divergent Berry curvature-a local manifestation of the geometric properties of electronic wavefunctions-at Weyl points. [ABSTRACT FROM AUTHOR]

Performance of magnetized liner inertial fusion (MagLIF) experiments is highly dependent on transport processes including magnetized heat flows and magnetic flux losses. Magnetohydrodynamic simulations used to model these experiments require a choice of model for the transport coefficients, which are the constants of proportionality relating driving terms, such as temperature gradients and currents, to the associated heat and magnetic field transport. The coefficients have been the subject of repeated recalculation using various methods throughout the years. Using a semi-analytic MagLIF model [McBride and Slutz, Phys. Plasmas 22, 052708 (2015)], we compare models for the transport coefficients provided by Braginskii [Reviews of Plasma Physics, edited by M. A. Leontovich (Consultants Bureau, New York, 1965), Vol. 1, p. 205], Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], Ji and Held [Phys. Plasmas 20, 042114 (2013)], Davies et al. [Phys. Plasmas 28, 012305 (2021)], and Sadler et al. [Phys. Rev. Lett. 126, 075001 (2021)]. The choice of model modifies magnetic-flux losses caused by the Nernst thermoelectric effect and thermal conduction losses. We present simulated results from parameter scans conducted in order to compare the effects of the different models on parameters of interest in MagLIF. In some regions of parameter space, discrepancies of up to 38% are found in integrated quantities like the fusion yield. These results may serve as a guide for experimental validation of the various models, particularly as laser preheat energies and initial axial field strengths are increased on MagLIF experiments. [ABSTRACT FROM AUTHOR]

The large Nernst effect is advantageous for developing transverse Nernst thermoelectric generators or Ettingshausen coolers within a single component, avoiding the complexity of electron- and hole-modules in longitudinal Seebeck thermoelectric devices. We report a large Nernst signal reaching 130 μV/K at 8 K and 13 T in the layered metallic antiferromagnet EuAl2Si2. Notably, this large transverse Nernst thermopower is two orders of magnitude greater than its longitudinal counterpart. The Nernst coefficient peaks around 4 and 8 K at 3 and 13 T, respectively. At similar temperatures, both the Hall coefficient and the Seebeck signal change sign. Additionally, nearly compensated electron- and hole-like carriers with high mobility (∼ 4000 cm2/V s at 4 K) are revealed from the magnetoconductivity. These findings suggest that the large Nernst effect and vanishing Seebeck thermopower in EuAl2Si2 are due to the compensated electron- and hole-like bands, along with the high mobility of the Weyl band near the Fermi level. Our results underscore the importance of band compensation and topological fermiology in achieving large Nernst thermopower and exploring potential Nernst thermoelectric applications at low temperatures. [ABSTRACT FROM AUTHOR]

The large Nernst effect is advantageous for developing transverse Nernst thermoelectric generators or Ettingshausen coolers within a single component, avoiding the complexity of electron- and hole-modules in longitudinal Seebeck thermoelectric devices. We report a large Nernst signal reaching 130 μV/K at 8 K and 13 T in the layered metallic antiferromagnet EuAl2Si2. Notably, this large transverse Nernst thermopower is two orders of magnitude greater than its longitudinal counterpart. The Nernst coefficient peaks around 4 and 8 K at 3 and 13 T, respectively. At similar temperatures, both the Hall coefficient and the Seebeck signal change sign. Additionally, nearly compensated electron- and hole-like carriers with high mobility (∼ 4000 cm2/V s at 4 K) are revealed from the magnetoconductivity. These findings suggest that the large Nernst effect and vanishing Seebeck thermopower in EuAl2Si2 are due to the compensated electron- and hole-like bands, along with the high mobility of the Weyl band near the Fermi level. Our results underscore the importance of band compensation and topological fermiology in achieving large Nernst thermopower and exploring potential Nernst thermoelectric applications at low temperatures. [ABSTRACT FROM AUTHOR]

Transverse thermoelectric conversion phenomena including the anomalous Ettingshausen effect (AEE) and anomalous Nernst effect (ANE) in magnetic materials are actively investigated to realize versatile cooling and energy harvesting technologies. However, further improvement of the thermoelectric performance of AEE and ANE is still required, and most research efforts have focused on material exploration. Here, a new approach to improve the transverse thermoelectric conversion performance through interface engineering is reported by focusing on the transverse thermoelectric phenomena that output heat currents. A longitudinal charge current in a ferromagnetic metal Ni/nonmagnetic insulator Bi2WO6 hybrid‐structure induces a larger transverse heat current than that of AEE in a Ni single‐layer. It is indicated that the enhancement of the transverse thermoelectric conversion is due to the generation of a heat current concomitant with a spin current induced at the Ni/Bi2WO6 interface. This finding demonstrates that the interface of a magnetic metal/nonmagnetic insulator has a potential to improve the transverse thermoelectric performance, extending the applicability of nonmagnetic insulators to the field of spin caloritronics and thermoelectrics. [ABSTRACT FROM AUTHOR]

The influence of sample geometry on various measured physical properties (including the magneto-Seebeck effect, Nernst effect, magnetoresistance effect, Hall effect, and thermal conductivity) in the presence of a magnetic field was examined using a polycrystalline Bi-Sb sample. The sample, consisting of polycrystalline Bi88Sb12, was prepared through spark plasma sintering and subsequent annealing. Measurements of the physical properties were conducted under a magnetic field of 5 T, and the obtained values were compared with simulated results derived using the finite element method for different sample geometries. Distinct shapes were found to be necessary for accurate measurements, with each physical property requiring a specific aspect ratio of sample length (l) to width (w). These ratios were determined to be l/w > 0.57, 2.9, 4.2, 1.2, and 3.1 for the magnetoresistance, Hall, two-wire magneto-Seebeck, four-wire magneto-Seebeck, and Nernst effects, respectively. Additionally, to achieve a minimal error of less than 2% in thermal conductivity measurement, a thermal conductance ratio of Ks/Kw > 27 was necessary, where Ks and Kw denote the thermal conductance of the sample and lead wire, respectively. [ABSTRACT FROM AUTHOR]

The transverse thermoelectric effect based on the anomalous Nernst effect (ANE) has attracted attention, especially for thermoelectric and spintronic applications. Fe 3 X (X = Ga, Al) is known to exhibit a large ANE at room temperature owing to the topological electronic band structure so-called nodal web. Here, we systematically investigate ANE in the polycrystalline Fe3Ga1−xAlx and Fe3Al1−xSix. Despite significant chemical substitutions, a very robust feature of the large ANE − S y x ∼ 5.7 μ V/K is found for Fe3Ga1−xAlx (0 ≲ x ≲ 0.6), exhibiting a striking x independent nodal web contribution. Since aluminum is more low-cost and abundant than gallium, our results indicate Fe3Ga1−xAlx (x ∼ 0.6) should be suitable for large-scale thermoelectric applications. [ABSTRACT FROM AUTHOR]

The distinctive properties of topological semimetals, including linear band dispersion and compensated electron‐hole carriers, have positioned these materials at the forefront of research in power generation and solid‐state cooling due to their remarkable magneto‐thermoelectric performance. In this work, the transverse thermoelectric characteristics of the topological semimetal NbAs2 are studied. Specifically, under a magnetic field of 9 T, the Nernst coefficient displays a linear and unsaturated trend, reaching a peak of 600 µV K−1 at 35 K. Consequently, this engenders a substantial transverse power factor (tPF) of 850 µW cm−1 K−2 under a 5 T magnetic field. The exceptional attributes of NbAs2 driven by its remarkably high carrier mobility and compensated electron‐hole concentration near the Fermi level are revealed by band structure analysis based on theoretical calculations and quantum oscillations. This work not only underscores the immense potential of topological semimetals as transverse thermoelectric materials for niche applications where magnetic fields exist but also provides valuable guidance for the discovery and optimization of topological materials for promising thermoelectric performance. [ABSTRACT FROM AUTHOR]

In this study, within the framework of electron magnetohydrodynamics, taking into account thermomagnetic phenomena, we obtained a new large-scale instability of the α -effect type, which ensures the generation of large-scale vortex and magnetic fields. This instability occurs in a flat layer of temperature-stratified plasma under the influence of an external uniform magnetic field inclined relative to the layer, combined with a small-scale external force having zero helicity. The external force is presented as a source of small-scale oscillations in the speed of electrons with a low Reynolds number R ≪ 1. The presence of a small parameter in the system allowed us to apply the method of multiscale asymptotic expansions to derive nonlinear equations for vortex and magnetic disturbances. These equations were obtained in third-order Reynolds number. Using solutions for the velocity field in zero order in Reynolds number, we determined the average helicity H = v 0 · rot v 0 ¯ and its relation to the α -effect. A necessary condition for the generation of average helicity in stratified magnetized plasma is the inclined orientation of the external magnetic field and the presence of a small-scale force. A new effect related to the influence of thermal force (the Nernst effect) on large-scale instability is discussed. It is shown that an increase in the Nernst parameter leads to a decrease in the amplification factor α and thereby prevents the development of large-scale instability. With the help of numerical analysis, stationary solutions to the vortex and magnetic dynamo equations in the form of localized structures like nonlinear waves of the Beltrami were obtained. [ABSTRACT FROM AUTHOR]

The distinctive properties of topological semimetals, including linear band dispersion and compensated electron‐hole carriers, have positioned these materials at the forefront of research in power generation and solid‐state cooling due to their remarkable magneto‐thermoelectric performance. In this work, the transverse thermoelectric characteristics of the topological semimetal NbAs2 are studied. Specifically, under a magnetic field of 9 T, the Nernst coefficient displays a linear and unsaturated trend, reaching a peak of 600 µV K−1 at 35 K. Consequently, this engenders a substantial transverse power factor (tPF) of 850 µW cm−1 K−2 under a 5 T magnetic field. The exceptional attributes of NbAs2 driven by its remarkably high carrier mobility and compensated electron‐hole concentration near the Fermi level are revealed by band structure analysis based on theoretical calculations and quantum oscillations. This work not only underscores the immense potential of topological semimetals as transverse thermoelectric materials for niche applications where magnetic fields exist but also provides valuable guidance for the discovery and optimization of topological materials for promising thermoelectric performance. [ABSTRACT FROM AUTHOR]

Recently, the study of quantum materials through thermal characterization methods has attracted much attention. These methods, although not as widely used as electrical methods, can reveal intriguing physical properties in materials that are not detectable by electrical methods, particularly in electrical insulators. A fundamental understanding of these physical properties is critical for the development of novel applications for energy conversion and storage, quantum sensing and quantum information processing. In this review, we introduce several commonly used thermal characterization methods for quantum materials, including specific heat, thermal conductivity, thermal Hall effect, and Nernst effect measurements. Important theories for the thermal properties of quantum materials are discussed. Moreover, we introduce recent research progress on thermal measurements of quantum materials. We highlight experimental studies on probing the existence of quantum spin liquids, Berry curvature, chiral anomaly, and coupling between heat carriers. We also discuss the work on investigating the quantum phase transitions and quasi-particle hydrodynamics using thermal characterization methods. These findings have significantly advanced knowledge regarding novel physical properties in quantum materials. In addition, we provide some perspectives on further investigation of novel thermal properties in quantum materials. [ABSTRACT FROM AUTHOR]

Abstract The Nernst effect is a fundamental thermoelectric conversion phenomenon that was deemed to be possible only in systems with magnetic field or magnetization. In this work, we propose a novel dynamical chiral Nernst effect that can appear in two-dimensional van der Waals materials with chiral structural symmetry in the absence of any magnetic degree of freedom. This unconventional effect is triggered by time variation of an out-of-plane electric field, and has an intrinsic quantum geometric origin linked to not only the intralayer center-of-mass motion but also the interlayer coherence of electronic states. We demonstrate the effect in twisted homobilayer and homotrilayer transition metal dichalcogenides, where the strong twisted interlayer coupling leads to sizable intrinsic Nernst conductivities well within the experimental capacity. This work suggests a new route for electric control of thermoelectric conversion.

A Heat Flux Sensor (HFS) facilitates the visualization of heat flow, unlike a temperature sensor, and is anticipated to be a key technology in managing waste heat. Recently, an HFS utilizing the Anomalous Nernst Effect (ANE) has been proposed garnering significant interest in enhancing the transverse thermopower. However, ideal materials for HFS not only require a large transverse thermopower but also meet several criteria including low thermal conductivity and a bipolar nature of the transverse thermopower, especially a negative transverse thermopower. In this study, we have investigated ANE in amorphous ferrimagnetic GdCo alloys, revealing their numerous advantages as HFS materials. These include a large bipolar transverse thermopower, extremely low thermal conductivity, large negative sensitivity, versatility for deposition on various substrates, and a small longitudinal thermopower. These qualities position GdCo films as promising candidates for the advancement of HFS technology. [ABSTRACT FROM AUTHOR]

Heat flux sensors (HFS) have attracted significant interest for their potential in managing waste heat efficiently. A recently proposed HFS, which works on the basis of the anomalous Nernst effect (ANE), offers several advantages in its simple structure leading to easy fabrication, low cost, and reduced thermal resistance. However, enhancing sensitivity through traditional material selection is now challenging due to a small number of materials satisfying the required coexistence of a large transverse thermopower and low thermal conductivity. In this study, by utilizing composite structures and optimizing the device geometry, we have achieved a substantial improvement in the sensitivity of an ANE-based HFS. We developed composite structures comprised of a plastic substrate with an uneven surface and three-dimensional (3D) uneven TbCo films, fabricated using nanoimprint techniques and sputtering. This approach resulted in a sensitivity that is approximately four times greater than that observed in previous studies. Importantly, this method is independent of the material properties and can significantly enhance the sensitivity. Our findings could lead to the development of highly sensitive HFS devices and open avenues for the fabrication of 3D devices. [ABSTRACT FROM AUTHOR]

Presented work concerns thermally activated 2D materials inducing an electric field in the presence of a magnetic field. The thermomagnetic Nernst effect combines these quantities, and several works reveal results that could be used for validation of the experimental setup before investigations of other structures with potential thermomagnetic effects. The paper shows experimental studies on the thermomagnetic Nernst effect observed in pure nickel samples. The scope of experimental studies covers relationships of the sensitivity of the Nernst coefficient to magnetic field ranging to 1 T and temperature gradient above room temperature. The obtained results were discussed in relation to the referenced works. [ABSTRACT FROM AUTHOR]

It is shown that many anomalies observed in underdoped cuprates, including anomalous spectral weight transfer and a large pseudogap, appear to have a common nature due to both the cluster structure of the underdoped phase and the specific mechanism of superconducting pairing. The combined action of these factors leads to the fact that at a temperature T lying in a certain temperature range Tc < T < T*, the crystal contains small isolated clusters that can exist both in superconducting and normal states, randomly switching between them. In this case, below Tc with a very high probability, the cluster is in a superconducting state, and above T*, it is in a normal state, and the interval Tc < T < T* is the region of existence of the so-called pseudogap phase. The temperatures Tc and T* for YBa2Cu3O6+δ were calculated depending on the doping level δ. The calculation results are in good agreement with the experiment without the use of fitting parameters. At a given T in the same temperature range, the time sequence of randomly arising superfluid density pulses from each cluster can be represented as a random process. The effective width Δωeff of the spectrum of such a random process will be determined by a correlation time, i.e., the characteristic time between successive on/off superconductivity in two different clusters. This time, according to the estimate, is ~ 10−15 s, which corresponds to Δωeff ~ 1 eV and explains the effect of spectral weight transfer to the high-frequency region. This approach also makes it possible to explain other anomalies observed in the vicinity of Tc: the reversibility of magnetization curves in a certain temperature range below Tc, the anomalous Nernst effect, and anomalous diamagnetism above Tc. [ABSTRACT FROM AUTHOR]

The Nernst effect is a fundamental thermoelectric conversion phenomenon that was deemed to be possible only in systems with magnetic field or magnetization. In this work, we propose a novel dynamical chiral Nernst effect that can appear in two-dimensional van der Waals materials with chiral structural symmetry in the absence of any magnetic degree of freedom. This unconventional effect is triggered by time variation of an out-of-plane electric field, and has an intrinsic quantum geometric origin linked to not only the intralayer center-of-mass motion but also the interlayer coherence of electronic states. We demonstrate the effect in twisted homobilayer and homotrilayer transition metal dichalcogenides, where the strong twisted interlayer coupling leads to sizable intrinsic Nernst conductivities well within the experimental capacity. This work suggests a new route for electric control of thermoelectric conversion. [ABSTRACT FROM AUTHOR]

Topological magnets (TMs) with the coupled topology of electronic band structures and spin configuration have exhibited exotic transport properties that are overwhelmingly appealing for transverse thermoelectric applications. Despite the continuous discovery of TMs in recent years, the development of Nernst generators has much lagged. Here, high‐performance Nernst generators are developed utilizing polycrystalline topological Heusler bulk magnets. Benefiting from the robustness of topological effect to grain boundary scattering, polycrystalline Co2MnGa is found to exhibit a large Nernst thermopower of ≈6.5 µV K−1 at 300 K, which is comparable to the previously reported record value in its single crystal. The developed Nernst generators thereby exhibit excellent performance with an output voltage of 5.4 mV and power of 14.3 µW, significantly higher than that of Nernst thermopiles assembled using conventional ferromagnets. These results pave the way to advancing TMs with intrinsically large Berry curvature for transverse thermoelectric applications. [ABSTRACT FROM AUTHOR]

Vortices in superconductors can help identify emergent phenomena but certain fundamental aspects of vortices, such as their entropy, remain poorly understood. Here, we study the vortex entropy in underdoped Bi2Sr2CaCu2O8+x by measuring both magneto-resistivity and Nernst effect on ultrathin flakes (≤2 unit-cell). We extract the London penetration depth from the magneto-transport measurements on samples with different doping levels. It reveals that the superfluid phase stiffness ρs scales linearly with the superconducting transition temperature Tc, down to the extremely underdoped case. On the same batch of ultrathin flakes, we measure the Nernst effect via on-chip thermometry. Together, we obtain the vortex entropy and find that it decays exponentially with Tc or ρs. We further analyze the Nernst signal above Tc in the framework of Gaussian superconducting fluctuations. The combination of electrical and thermoelectric measurements in the two-dimensional limit provides fresh insight into high temperature superconductivity. The authors study the vortex entropy in ultrathin flakes of the underdoped cuprate superconductor Bi2Sr2CaCu2O8+x by measuring both magneto-resistivity and Nernst effect. They find that, while the superfluid phase stiffness varies linearly with Tc, the vortex entropy decreases exponentially at lower Tc. [ABSTRACT FROM AUTHOR]

Sm-Co bulk alloys are well-known permanent magnets having large remanent magnetizations and coercive forces and are widely used in many industrial products. Recently, a large transverse thermoelectric conversion was observed for SmCo5 over a wide temperature range in the absence of magnetic fields. The large thermoelectric conductivity tensors (αxy) was also confirmed by the first-principles density functional theory (DFT) calculations. In this study, we predicted further enhancement of the αxy by including Ni in Co site of SmCo5. We showed that the αxy of Sm(Co1−xNix)5 increases with increasing the Ni ratio and takes the maximum value αxy = 11.3 A K−1 m−1 around x = 0.08 at 300 K, which is about 77% enhancement of αxy = 6.4 A K−1 m−1 in SmCo5. We clarified that the band proximity points near the nodal line of Sm(Co0.92Ni0.08)5 are the main contributing factor to the large Berry curvature, providing the steep slope of the energy dependence in the anomalous Hall conductivity around the Fermi energy. [ABSTRACT FROM AUTHOR]

Sm-Co bulk alloys are well-known permanent magnets having large remanent magnetizations and coercive forces and are widely used in many industrial products. Recently, a large transverse thermoelectric conversion was observed for SmCo5 over a wide temperature range in the absence of magnetic fields. The large thermoelectric conductivity tensors (αxy) was also confirmed by the first-principles density functional theory (DFT) calculations. In this study, we predicted further enhancement of the αxy by including Ni in Co site of SmCo5. We showed that the αxy of Sm(Co1−xNix)5 increases with increasing the Ni ratio and takes the maximum value αxy = 11.3 A K−1 m−1 around x = 0.08 at 300 K, which is about 77% enhancement of αxy = 6.4 A K−1 m−1 in SmCo5. We clarified that the band proximity points near the nodal line of Sm(Co0.92Ni0.08)5 are the main contributing factor to the large Berry curvature, providing the steep slope of the energy dependence in the anomalous Hall conductivity around the Fermi energy. [ABSTRACT FROM AUTHOR]

Transverse thermoelectric effect, the conversion of longitudinal heat current into transverse electric current, or vice versa, offers a promising energy harvesting technology. Materials with axis-dependent conduction polarity, known as p × n-type conductors or goniopolar materials, are potential candidate, because the non-zero transverse elements of thermopower tensor appear under rotational operation, though the availability is highly limited. Here, we report that a ternary metal LaPt2B with unique crystal structure exhibits axis-dependent thermopower polarity, which is driven by mixed-dimensional Fermi surfaces consisting of quasi-one-dimensional hole sheet with out-of-plane velocity and quasi-two-dimensional electron sheets with in-plane velocity. The ideal mixed-dimensional conductor LaPt2B exhibits an extremely large transverse Peltier conductivity up to ∣αyx∣ = 130 A K−1 m−1, and its transverse thermoelectric performance surpasses those of topological magnets utilizing the anomalous Nernst effect. These results thus manifest the mixed-dimensionality as a key property for efficient transverse thermoelectric conversion. The conversion between longitudinal heat flow and transverse charge current is a promising energy harvesting technology. Here, the authors show the large transverse thermoelectric effect induced by the mixed-dimensionality of Fermi surfaces. [ABSTRACT FROM AUTHOR]

The ordinary Nernst effect enables large transverse thermoelectric conversion in semimetals, but its operation requires the application of an external magnetic field. In this study, we propose a transverse thermoelectric conversion module structure with embedded permanent magnets and demonstrate thermoelectric power generation by the ordinary Nernst effect in the absence of an external magnetic field. In our prototype module comprising alternately stacked Bi88Sb12 slabs and Nd2Fe14B-type permanent magnets, the stray magnetic field generated by the remanent magnetization of the Nd2Fe14B-type magnets is always applied to the Bi88Sb12 slabs, and a power of 13.2 μW is generated due to the ordinary Nernst effect at a temperature difference of 120 K and average temperature of 260 K at zero external field. This thermoelectric module concept will contribute to the further development of transverse thermoelectric conversion technologies utilizing permanent magnets. [ABSTRACT FROM AUTHOR]

Background. The well-known quantum Hall effect observed in two-dimensional current conductors placed in a transvers magnetic field is due to the magnetic quantization of cyclotron orbits of charge carriers, leading to the appearance of Landau levels in theiz energy spectrum. This, in turn, causes quantization of the Hall resistance. Previously, we showed that in narrow nanowires (for example, in graphene nanoribbons), the effect of magnetic quantization is superimposed on the effect dimensional quantization, which also leads to quantization of the Hall and magnetoresistance coefficients. In this regard, it is of interest to study the influence of dimensional and magnetic quantization on the nature of the flow and other transfer phenomena that occur in two-dimensional conductors placed in a transverse magnetic field. The purpose of this work is to study galvanothermomagnetic phenomena on this subject: Nernst effects and thermomagnetic EMF. Materials and methods. The objects of research are graphene nanoribbons with metallic properties with zigzagtype edges less than 100 nm wide and a length not exceeding 1 μm (the ballistic path length of electrons in graphene). Well-known theoretical methods of quantum physics, crystallography and quantum theory of transport phenomena in two-dimensional electron gas were used. Results. Explicit expressions for the quanta of the Nernst coefficients and thermomagnetic EMF have been obtained, which allows us to take a fresh look at well-known galvanothermomagnetic phenomena and use the results obtained in the creation of nanoscale technical devices whose operation is based on these phenomena. Conclusions. It is shown that combined size and magnetic quantization of electronic states localized in narrow graphene nanoribbons leads to the emergence of the quantum Nernst effect and the appearance of quanta of the linear value of the Nernst coefficient, the strength of the transverse Nernst current, and the coefficient of the longitudinal absolute thermomagnetic EMF.

Anomalous Nernst effect of epitaxial Fe4N films on MgO(001), MgAl2O4(MAO)(001), and SrTiO3(STO)(001) substrates grown by molecular beam epitaxy was investigated. Moderately large anomalous Nernst coefficients (SANE) of 1.4 and 1.7 μV/K were obtained in the Fe4N films on the MgO(001) and MAO(001) substrates, respectively, and large anomalous Hall angles (∼0.06) and transverse thermoelectric conductivities [∼1.3 A/(m K)] were derived from the experimental results. On the other hand, a large effective SANE of 2.8 μV/K was obtained in the Fe4N film on the STO(001) substrate. The origin of the enhanced effective SANE is the negatively large Seebeck coefficient (SSE) in an oxygen deficient STO layer near the surface of the STO substrate. This indicates that it is possible to enhance the effective SANE of ferromagnetic materials by utilizing adjacent materials with large |SSE| such as the oxygen deficient STO layer. [ABSTRACT FROM AUTHOR]

The Nernst effect describes a linear relationship between orthogonal components of a magnetic field, a temperature gradient, and a resulting transverse electric field. A non-local electrical measurement, where injection and detection are physically separated on the specimen, serves as a versatile and effective platform for measuring spin and thermal effects due to the avoided interference with a charge current directly. Here, we quantify the Nernst coefficient of Pt, a common material for spin injection in non-local geometries, by a non-local electrical measurement under modulated temperature and magnetic field and finite element analysis for modeling heat transfer. We determine the Nernst coefficient of Pt from room temperature (8.56 nV K − 1 T − 1 ) to 10 K (29.3 nV K − 1 T − 1 ). Beyond the quantification of the Nernst coefficient, our results show that careful consideration of the thermal properties of the thermal sink and electrode materials is needed when making an interpretation of non-local electrical measurements. [ABSTRACT FROM AUTHOR]

In this work, a measurement setup to study the Seebeck and Nernst effect at high temperatures and high magnetic fields is introduced and discussed. The measurement system allows for simultaneous measurements of both thermoelectric effects up to 700 K and magnetic fields up to 12 T. Based on theoretical concepts, measurement equations are derived that counteract constant spurious offset voltages and, therefore, inhibit systematic errors in the measurement setup. The functionality is demonstrated on polycrystalline samples of elemental bismuth as well as various full-Heusler materials, exhibiting an anomalous Nernst effect. In all samples, the measured Seebeck and Nernst coefficients align excellently with the reported values. This allows future research to substantially extend the measured temperature and field intervals, commonly limited to temperatures below room temperature. For the first time, the thermoelectric and thermomagnetic properties of these materials are reported up to temperatures of 560 K. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect (ANE) has garnered significant interest for practical applications, particularly in energy harvesting and heat flux sensing. For these applications, it is crucial for the module to operate without an external magnetic field, necessitating a combination of a large ANE and a substantial coercive force. However, most materials exhibiting a large ANE typically have a relatively small coercive force. In our research, we have explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the coercive force peaks at the magnetization compensation point (MCP). We observed that transverse Seebeck coefficients are amplified with Tb doping, reaching more than 1.0 μV/K over a wide composition range near the MCP, which is three times greater than that of pure Co. Our findings indicate that this enhancement is primarily due to direct conversion, a product of the transverse thermoelectric component and electrical resistivity. TbCo films present several significant advantages for practical use: a large ANE, the capability to exhibit both positive and negative ANE, the flexibility to be deposited on any substrate due to their amorphous nature, a low thermal conductivity, and a large coercive force. These attributes make TbCo films a promising material for advancing ANE-based technologies. [ABSTRACT FROM AUTHOR]

Functional materials such as magnetic, thermoelectric, and battery materials have been revolutionized through nanostructure engineering. However, spin caloritronics, an advancing field based on spintronics and thermoelectrics with fundamental physics studies, has focused only on uniform materials without complex microstructures. Here, we show how nanostructure engineering enables transforming simple magnetic alloys into spin-caloritronic materials displaying significantly large transverse thermoelectric conversion properties. The anomalous Nernst effect, a promising transverse thermoelectric phenomenon for energy harvesting and heat sensing, has been challenging to utilize due to the scarcity of materials with large anomalous Nernst coefficients. We demonstrate a remarkable ~ 70% improvement in the anomalous Nernst coefficients (reaching ~ 3.7 µVK−1) and a significant ~ 200% enhancement in the power factor (reaching ~ 7.7 µWm−1K−2) in flexible Fe-based amorphous materials by nanostructure engineering without changing their composition. This surpasses all reported amorphous alloys and is comparable to single crystals showing large anomalous Nernst effect. The enhancement is attributed to Cu nano-clustering, facilitating efficient transverse thermoelectric conversion. This discovery advances the materials science of spin caloritronics, opening new avenues for designing high-performance transverse thermoelectric devices for practical applications. Nanostructure engineering enables transforming simple magnetic alloys into spincaloritronic materials with large transverse thermoelectric conversion. This has led to a high anomalous Nernst coefficient in flexible Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]

A superconductor-insulator transition (SIT) in two dimensions is a prototypical quantum phase transition (QPT) with a clear quantum critical point (QCP) at zero temperature (T = 0). The SIT is induced by a field B and observed in disordered thin films. In some of weakly disordered or crystalline thin films, however, an anomalous metallic (AM) ground state emerges over a wide B range between the superconducting and insulating phases. It remains a fundamental open question how the QPT picture of the SIT is modified when the AM state appears. Here we present measurements of the Nernst effect N, which has great sensitivity to the fluctuations of the superconducting order parameter. From a thorough contour map of N in the B-T plane, we found a thermal-to-quantum crossover line of the superconducting fluctuations, a so-called ghost-temperature line associated with the QPT, as well as a ghost-field line associated with a thermal transition. The QCP is identified as a T = 0 intercept of the ghost-temperature line inside the AM state, which verifies that the AM state is a broadened critical state of the SIT. The authors present Nernst measurements on a 2D film of amorphous MoxGe1−x, which shows a magnetic-field-induced superconductor-metal-insulator transition. The intermediate metal phase is known as the "anomalous metal" (AM) state. The authors conclude that the AM state originates from broadening of the superconductor-insulator transition. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect (ANE), as a three-dimensional thermoelectric effect in ferromagnetic materials, is expected to break through the limitations of the traditional Seebeck effect, thereby improving thermoelectric conversion efficiency. This study reports an anisotropic anomalous Nernst effect in metallic nickel assembled by the alignment of nanowires. It is found that the ANE voltage varies with the angle to the alignment direction of nanowires within the in-plane of metallic nickel. The ANE voltage reaches 530 nV under a longitudinal temperature difference of 23 K when the magnetic field is applied parallel to the alignment direction of nanowires, which is 143% of its value in the vertical direction. This design concept for anisotropic materials may provide a novel path to enhanced thermoelectric efficiency in ANE-based thermoelectric devices. [ABSTRACT FROM AUTHOR]

A transverse thermoelectric generator for magnetic-field-free and high-density power generation utilizing the anomalous Nernst effect is constructed and its performance is characterized. By alternately stacking two different permanent magnets with the large coercivity and anomalous Nernst coefficients of opposite sign, transverse thermoelectric voltage and power can be generated in the absence of external magnetic fields and enhanced owing to a thermopile structure without useless electrode layers. In the permanent-magnet-based stack, the magnetic attractive force enables easy construction of the thermopile structure with a high fill factor. In this study, we construct a bulk module consisting of 12 pairs of SmCo5- and Nd2Fe14B-type permanent magnets having positive and negative anomalous Nernst coefficients, respectively, whose fill factor reaches ∼80%, whereas that of conventional thermoelectric modules based on the Seebeck effect is typically 30%–60%. We demonstrate magnetic-field-free anomalous Nernst power generation up to 177 µW at a temperature difference of 75 K around room temperature, which corresponds to the largest anomalous Nernst power density of 65 µW/cm2. The presented module structure concept will provide a design guideline for high-performance transverse thermoelectric power generation. [ABSTRACT FROM AUTHOR]

The capability of magnons to hybridize and strongly couple with diverse excitations offers a promising avenue for realizing and controlling emergent properties that hold significant potential for applications in devices, circuits, and information processing. In this Letter, we present recent theoretical and experimental developments in magnon-based hybrid systems, focusing on the combination of magnon excitation in an antiferromagnet with other excitations, namely, plasmons in a topological insulator, phonons in a 2D antiferromagnetic (2D AFM), and photons. The existence of THz frequency magnons, plasmons, and phonons makes magnon-based hybrid systems particularly appealing for high-operating-speed devices. In this context, we explore several directions to advance magnon hybrid systems, including strong coupling between a surface plasmon and magnon polariton in a topological insulator /AFM bilayer, a giant spin Nernst effect induced by magnon–phonon coupling in 2D AFMs, and control of magnon–photon coupling using spin torque. [ABSTRACT FROM AUTHOR]

The anomalous Nernst effect (ANE) has been under consideration for potential transverse thermoelectric applications. However, the utilized material systems are generally limited to chemically ordered crystals with notable features of nontrivial band topology and/or strong spin–orbit coupling, such as topological ferromagnets and antiferromagnets. In this study, we present the observation of a robust room-temperature ANE in a chemically disordered ferromagnet, specifically an A1-type FexPt100−x alloy. The observed anomalous Nernst thermopower Sxy (∼1.6 μV/K) remains stable over a wide range of thicknesses (6 ≤ t ≤ 100 nm) and compositions (46 ≤ x ≤ 67), which is in stark contrast to the common situation in topological ferromagnets. This behavior can be attributed to both the large anomalous Nernst conductivity αxy (∼1.3 A K−1 m−1), originating from Berry phase effects, as well as the significant Seebeck-driven anomalous Hall effect that modulates its action through mean-free-path and two-carrier models. [ABSTRACT FROM AUTHOR]

Magnetic position sensors have extensive applications in various industrial sectors and consumer products. However, measuring angles in the full range of 0–360° in a wide field range using a single magnetic sensor remains a challenge. Here, we propose a magnetic position sensor based on a single Wheatstone bridge structure made from a single ferromagnetic layer. By measuring the anisotropic magnetoresistance (AMR) signals from the bridge and two sets of anomalous Nernst effect (ANE) signals from the transverse ports on two perpendicular Wheatstone bridge arms concurrently, we show that it is possible to achieve 0–360° angle detection using a single bridge sensor. The combined use of AMR and ANE signals allows a mean angle error in the range of 0.51–1.05° within a field range of 100 Oe–10,000 Oe to be achieved. [ABSTRACT FROM AUTHOR]

Conversion of thermal to electrical energy has been a subject of intense study for well over two centuries. Despite steady progress throughout the past several decades, solid-state thermoelectric (TE) energy conversion devices remain adequate only for niche applications. One appealing option for circumventing the limits of conventional TE physics is to utilize phenomena where flows of heat and charge are perpendicular, the so-called "transverse" geometry. In this Tutorial, we discuss recent advances behind new ways to generate large transverse thermoelectric voltages, such as the spin Seebeck and Nernst effects, as well as Weyl physics. We provide suggestions for how these mechanisms might be enhanced and implemented into high-efficiency, next generation transverse TE devices. We also discuss best practices for accurate measurement and reporting of transverse thermoelectric material properties, including a case study of a round robin spin Seebeck coefficient measurement. [ABSTRACT FROM AUTHOR]

The finite Berry curvature in topological materials can induce many subtle phenomena, such as the anomalous Hall effect (AHE), spin Hall effect (SHE), anomalous Nernst effect (ANE), non-linear Hall effect (NLHE) and bulk photovoltaic effects. To explore these novel physics as well as their connection and coupling, a precise and effective model should be developed. Here, we propose such a versatile model—a 3D triangular lattice with alternating hopping parameters, which can yield various topological phases, including kagome bands, triply degenerate fermions, double Weyl semimetals and so on. We reveal that this special lattice can present unconventional transport due to its unique topological surface states and the aforementioned topological phenomena, such as AHE, ANE, NLHE and the topological photocurrent effect. In addition, we also provide a number of material candidates that have been synthesized experimentally with this lattice, and discuss two materials, including a non-magnetic triangular system for SHE, NLHE and the shift current, and a ferromagnetic triangular lattice for AHE and ANE. Our work provides an excellent platform, including both the model and materials, for the study of Berry-curvature-related physics. [ABSTRACT FROM AUTHOR]

Recent discoveries of topological magnets have opened up diverse spintronic applications of large responses due to their unique band structures. A prominent example is the anomalous Nernst effect (ANE), a transverse magneto-thermoelectric phenomenon that produces an electromotive force orthogonal to the heat flux and magnetization. Unlike the Seebeck effect generating an electromotive force parallel to the heat flux, transverse thermoelectric properties of ANE well fit in the lateral configurations of devices fabricated through conventional thin-film fabrication processes. This feature enables distinct device applications through a simplified fabrication process, reduced production cost, extensive area coverage, and enhanced flexibility. In this study, we report the highest ANE ever recorded among all reported polycrystalline films to date by using a topological ferromagnet. In particular, we have fabricated high-quality polycrystalline thin films of the Weyl ferromagnet Co2MnGa that exhibit a large ANE of − 5.4 μV/K. By retaining a high film density, we demonstrate the sizable ANE in the films obtained using a simple fabrication process well suited for device developments. Establishing a thin-film fabrication technique capable of producing a giant ANE facilitates spintronic applications of the Weyl ferromagnet, including diverse ANE-based device applications. [ABSTRACT FROM AUTHOR]